Struct arrow::datatypes::Schema

pub struct Schema { /* fields omitted */ }

Describes the meta-data of an ordered sequence of relative types.

Note that this information is only part of the meta-data and not part of the physical memory layout.

Implementations

impl Schema

pub fn empty() -> Self

Creates an empty Schema

pub fn new(fields: Vec<Field>) -> Self

Creates a new Schema from a sequence of Field values.

Example

let field_a = Field::new("a", DataType::Int64, false);
let field_b = Field::new("b", DataType::Boolean, false);

let schema = Schema::new(vec![field_a, field_b]);

pub const fn new_with_metadata(
    fields: Vec<Field>,
    metadata: HashMap<String, String>
) -> Self

Creates a new Schema from a sequence of Field values and adds additional metadata in form of key value pairs.

Example

let field_a = Field::new("a", DataType::Int64, false);
let field_b = Field::new("b", DataType::Boolean, false);

let mut metadata: HashMap<String, String> = HashMap::new();
metadata.insert("row_count".to_string(), "100".to_string());

let schema = Schema::new_with_metadata(vec![field_a, field_b], metadata);

pub fn try_merge(schemas: impl IntoIterator<Item = Self>) -> Result<Self>

Merge schema into self if it is compatible. Struct fields will be merged recursively.

Example:

use arrow::datatypes::*;

let merged = Schema::try_merge(vec![
    Schema::new(vec![
        Field::new("c1", DataType::Int64, false),
        Field::new("c2", DataType::Utf8, false),
    ]),
    Schema::new(vec![
        Field::new("c1", DataType::Int64, true),
        Field::new("c2", DataType::Utf8, false),
        Field::new("c3", DataType::Utf8, false),
    ]),
]).unwrap();

assert_eq!(
    merged,
    Schema::new(vec![
        Field::new("c1", DataType::Int64, true),
        Field::new("c2", DataType::Utf8, false),
        Field::new("c3", DataType::Utf8, false),
    ]),
);

pub const fn fields(&self) -> &Vec<Field>

Returns an immutable reference of the vector of Field instances.

pub fn field(&self, i: usize) -> &Field

Returns an immutable reference of a specific Field instance selected using an offset within the internal fields vector.

pub fn field_with_name(&self, name: &str) -> Result<&Field>

Returns an immutable reference of a specific Field instance selected by name.

pub fn fields_with_dict_id(&self, dict_id: i64) -> Vec<&Field>

Returns a vector of immutable references to all Field instances selected by the dictionary ID they use.

pub fn index_of(&self, name: &str) -> Result<usize>

Find the index of the column with the given name.

pub const fn metadata(&self) -> &HashMap<String, String>

Returns an immutable reference to the Map of custom metadata key-value pairs.

pub fn column_with_name(&self, name: &str) -> Option<(usize, &Field)>

Look up a column by name and return a immutable reference to the column along with its index.

pub fn to_json(&self) -> Value

Generate a JSON representation of the Schema.

pub fn from(json: &Value) -> Result<Self>

Parse a Schema definition from a JSON representation.

pub fn contains(&self, other: &Schema) -> bool

Check to see if self is a superset of other schema. Here are the comparision rules:

• self and other should contain the same number of fields
• for every field f in other, the field in self with corresponding index should be a superset of f.
• self.metadata is a superset of other.metadata

In other words, any record conforms to other should also conform to self.

Trait Implementations

impl Clone for Schema

fn clone(&self) -> Schema

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Schema

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for Schema

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error> where
    __D: Deserializer<'de>, 

Deserialize this value from the given Serde deserializer.

impl Display for Schema

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq<Schema> for Schema

fn eq(&self, other: &Schema) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Schema) -> bool

This method tests for !=.

impl Serialize for Schema

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error> where
    __S: Serializer, 

Serialize this value into the given Serde serializer.

impl Eq for Schema

impl StructuralEq for Schema

impl StructuralPartialEq for Schema